In the current design of 3D-HEVC, when decoding a current picture, several new 3D-HEVC tools refer to pictures, which a) belong to a component different from the component of the current picture (where a component can be texture or depth); b) are included in the same access unit (AU) (where an AU contains all pictures of the same time instant with equal picture order count); and are c) not in the reference picture list of the current picture. More specifically:
1. When decoding a current depth picture, some tools refer to the texture reference pictures belonging to the same view and AU as the depth picture. Thus, the current component is depth and the reference component is texture.
2. When decoding a texture picture, some tools refer to the depth pictures belonging to the views of the texture reference pictures of the current texture picture and the AU of the current texture picture. Thus, the current component is texture and the reference component is depth.
See Example 1 in FIG. 1, which illustrates the inter-component prediction from depth to texture. FIG. 1 depicts a subset of layers of a 3D-HEVC multilayer bitstream and inter-component dependencies of a current picture. The current picture is picture 1 of layer 6. The current component is texture and the reference component is depth. The parameters sets SPS, VPS; pictures 0 of layers 1, 3, 5 and 6; pictures 1 of layers 1, 3, and 5; and the slice header of the current picture are decoded before decoding any coding units (CUs) of the current picture. When CU 0, CU1, and CU 2 of the current picture are decoded, inter-component prediction from pictures 1 of depth layers of views 2, 0, and 1, respectively, is performed.
In the current design tools using inter-component prediction are enabled or disabled for the current picture as follows:
If the current picture is a depth picture, the reference component is texture. Otherwise (the current picture is a texture picture), the reference component is depth.
Views which might be used for inter-component prediction of the current picture are derived from syntax elements in the VPS, SPS and the slice header of the current picture. In the following it is assumed that indices of these views are included in the list inCompRefViewIdcs.
If all of the following conditions are true, a particular tool is enabled for the current picture:                For each view i in inCompRefViewIdcs, the following is true:                    Syntax elements in the VPS signal that a reference component layer of view i is present in the bitstream and available as reference layer for the layer containing the current picture.                        The particular tool using inter-component prediction is enabled for the layer containing the current picture by SPS and/or the VPS enabling flags.        
Otherwise, the particular tool using inter-component prediction is disabled for current picture.
As an Example 2, see again FIG. 1: views that might be used for inter-component prediction from depth are derived as inCompRefViewIdcs={2, 1, 0}. For all views a depth layer is present in the bitstream, such that tools using inter-component from depth can be enabled for all CUs (0, 1 and 2) of the current picture.
The current method for enabling inter-component prediction has two issues:
First issue: The presence a reference component layer in the bitstream does not entail the presence of all its pictures. Thus, a particular picture of a present reference component layer can be missing, and inter-component prediction from this picture is still enabled.
See Example 3 in FIG. 2. In FIG. 2, depth layers are present in the bitstream for all views included in inCompRefViewIdcs={2, 1, 0}, such that inter-component prediction from depth is enabled for all CUs of the current layer. However, inter-component prediction for CU 1 in the current picture fails, since picture 1 of the depth layer of view 0 is missing.
Second issue: Not all reference component layers of views in inCompRefViewIdcs are included in the bitstream, such that inter-component prediction is disabled for all CUs of the current picture. However, inter-component could be applied for CUs of the current picture which refer the present pictures of reference component layers.
See Example 4 in FIG. 3. In FIG. 3, the depth layer of view 0 is not included in the bitstream.
Hence, not all depth layers of views included in inCompRefViewIdcs={2, 1, 0} are present in the bitstream, such that inter-component prediction is disabled for all CUs of the current picture. However, inter-component prediction from the depth layer of view 2 and the depth layer of view 1 for CU 0 and CU 2, respectively, could be applied.
The above issues may naturally also occur in 3D video codecs other than 3D-HEVC. Accordingly, there is a need for a 3D video codec supporting inter-component prediction which operates correctly in a wider range of possible settings accompanying the individual views with depth on the one and the enablement of inter-component prediction on the other hand.